In the past, in the CSD method, for example, a sol-gel method, in a case in which a PZT-based ferroelectric thin film (abbreviated to “PZT film”) was formed on a substrate, the limitation on the thickness of the thin film formed by coating a PZT-based ferroelectric thin film-forming sol-gel solution (abbreviated to “sol-gel solution”) once was approximately 100 nm. This is because, when a film having a thickness of more than 100 nm is calcined and fired, tensile stress generated in the PZT film is generated unevenly in the same film, and, consequently, cracking often occurs in the film.
Therefore, in order to obtain a PZT film having a film thickness of several μm, it is necessary to form a thinner layer, carry out coating several tens of times, and repeat calcination and firing. However, since the production efficiency decreases in such a method, the film-forming costs increase.
As a result, to deal with the above disadvantage, a sol-gel solution which uses propylene glycol as an organic solvent used for preparing a sol-gel solution and can produce a thick film having a thickness of 200 nm or more per layer when coated once is proposed (for example, refer to Patent Document 1). In addition, a method is proposed in which a macromolecule is added to a high-concentration sol-gel solution so as to alleviate tensile stress generated during film formation, whereby a thick layer can be coated by coating a sol-gel solution once (for example, refer to Non Patent Document J Sol-Gel Sci Technol (2008) 47:316-325).